A thermal insulating firebrick (ceramic porous body) is a porous lightweight refractory to which not only fire resistance but also thermal insulating property are imparted by forming a lot of bubbles inside a fire resistant material. A thermal insulating firebrick is used independently for a heating surface (for example, inner surface of a furnace) in some cases, and is used in combination with another fire resistant material as lining in other cases.
Hitherto, various production techniques for forming bubbles inside a fire resistant material have been established. For example, a technique in which pores are obtained by destroying combustibles by fire after molding and drying slurry containing a fire resistant powder such as ceramic powder, combustibles, and water, and a technique in which pores are obtained by blowing air or gas into slurry containing a fire resistant powder and water or generating gas inside slurry mixed with a gas generating material have been known.
In addition, production of a porous thermal insulating firebrick is also performed using a raw material originally having a high porosity, for example, such as diatomaceous earth, pearlite, and vermiculite as a main raw material. Among these, since a lot of fine pores are present in diatomaceous earth, a thermal insulating firebrick using diatomaceous earth as a main raw material is widely diffused as an excellent thermal insulating firebrick with a low thermal conductivity. However, diatomaceous earth cannot be used in a high temperature range exceeding 1,000° C. since the heat resistant temperature thereof is about 1,000° C. Therefore, in order to cope with use in a high temperature range exceeding 1,000° C., a production technique for producing a porous thermal insulating firebrick using a raw material excellent in heat resistance as a main raw material has been practically applied.
In Patent Literature 1, a porous molded body in which pores are contained in slurry containing ceramic powder and water, and a method for producing the porous molded body are disclosed. The porous molded body disclosed in Patent Literature 1 is produced in such a manner that slurry containing ceramic powder and water is stirred to form bubbles, the content and pore size of the bubbles (pores) in the slurry is adjusted by controlling stirring, and then the slurry is dried for solidification. This porous molded body is characterized in that the pore size inside the porous molded body is 1 mm or less and the porosity thereof is 60% or more, the pores are approximately homogenously distributed inside the porous molded body, and the shape of the porous molded body is imparted according to the purpose.
Since the porous molded body disclosed in Patent Literature 1 is a low density and high quality porous molded body including pores with a controlled pore size and distribution, the porous molded body can be preferably used for various purposes such as a lightweight constructional material, a thermal insulating material, a soundproof material, a seismic isolation material, a filter, a sensor, a catalyst support, and a biomaterial. However, the main object of the invention disclosed in Patent Literature 1 is to use the porous molded body as a filter or the like in which fluid passes through the pores. Accordingly, the following description is disclosed in Patent Literature 1. The technical meaning that a pore size inside a porous molded body is 1 mm or less and the porosity thereof is 60% or more is that properties of the porous molded body, such as fluid permeability, liquid absorbency, liquid storage property, and gas adsorptivity, are combined in a good balance. Controlling the pore size means that the properties (permeability coefficient of fluid, capillarity, specific surface area, and the like) of a porous member attributing to the pore size can be arbitrarily controlled.